First funding period: July 2016 - June 2020

Summary:

A hallmark of cell physiology is the coordination of signal transmission across space and time. Cells employ molecular switches to control all principal steps of their signaling pathways. The corresponding cellular responses are characterized by a wide spectrum of time scales ranging from milliseconds to hours. For example, ultrafast processes such as neurotransmission occur in milliseconds. Slower responses are protein secretion and receptor-proximal signaling occurring at a time scale of seconds to minutes. Global transcriptional modulation by the circadian clock is even slower with response times of hours. The identities and mechanisms of many cellular components acting as molecular switches such as kinases and phosphatases are known in detail, but it is poorly understood how they operate in space and time to regulate cellular responses at different time scales in living cells. On the one hand, this deficit can be overcome by the relatively recent development of adequate tools to acutely activate or deactivate molecular switches in living cells. On the other hand, the emerging availability of quantitative live cell imaging combined with super-resolution techniques now allows for experimental read-outs providing high spatio-temporal resolution. Therefore, a principal aim of this research network is to take advantage of a broad spectrum of novel chemical biology and optogenetic tools to study cellular signaling processes governed by molecular switches with sophisticated microscopic methods. Biological questions were selected to systematically compare a wide range from ultrafast (ms) to slow (hours) cellular responses. We aim at a quantitative description and dissection of individual steps of regulated protein secretion and endocytosis, ligand- and stress-dependent receptor down-stream signaling and the regulation of gene transcription and splicing in living cells. This goal will be achieved by quantitative measurement of the time-dependent localization, assembly and activation state of signaling molecules with appropriate temporal and spatial resolution in living cells, following controlled interference by light or by small molecules. As a long-term goal, these experimental data will be used to establish theoretical models aiming at a quantitative description of how living cells translate the activation states of a limited set of molecular switches into a broad spectrum of cellular responses. This will permit the discovery of principles that govern the spatio-temporal regulation of signaling networks.